Claim

Explore the chemical synthesis of a biofuel produced from algae and its comparisons with existing fuel sources

Bio-fuel

Bio-gasoline

Existing Fuel Source

Petroleum

Background

Explore the chemical synthesis of a biofuel produced from agae and its comparison with existing fuel sources

What are algal fuels?

Why are algal fuels being investigated?

Algal fuels are considered 'Third Generation' biofuels, developed to improve the viability of biomass derived fuels at large scale. Third generation fuels are derived from aquatic biomass, and therefore do not compete with traditional land based agriculture. Another advantage is reduced waste products due to lack of cellulose and fibrous materials. These fuels require more water than their predecessors, but can grow in high salinity environments, like the ocean.

(Brennan & Owende, 2010)
(Journal of Biotechnology and Bioengineering Research, 2024)

What fuels are created by algae

While third generation fuel sources can processed into ethanol, similarly to maize or sugar cane, their high oil and lipid content allows them to be refined into previously impractical fuel options.
Biogasoline is one of these, and is touted as a 'drop in replacement' for unleaded gasoline.

Well what is biogasoline?

Research question

How do does the collection and cracking processes differ between synthesis of gasoline and biogasoline, and how do the final products

Is biogasoline produced from algae viable to synthesise, and a complete "drop in replacement" for gasoline.

Categories of comparison

Aquisition and refinery of crude oil

Our current crude oil reserves are the result of organic matter pyrolysing underground over "millions of years" (Energy Education, n.d.-a).
Pyrolysis is the process of breaking down longer "heavy" hydrocarbon chains into smaller, "lighter" products in the absence of free oxygen molecules. In this case, the long molecules that make up the organic matter are broken down into more simple chains. Molecules not present in the shorter chains, such as oxygen, nitrogen, and hydrogen, form by-products such as (water), (ammonia), (carbon monoxide) and (carbon dioxide) (Australian Institute of Petroleum, n.d.).
Oil is pumped from "wells", stored in, and sold by the barrel (Energy Education, n.d.-a).
While the product collected is heterogeneous, and contains a huge variety of unusable hydrocarbons, further pyrolysis under controlled conditions and in the presence of a catalyst permits controlled reformation of the crude product into useful and refined fuels. These products can then be separated through fractional distillation.

(U.S. Energy Information Administration, n.d.)

Production of Bio Oil

How is algae produced

While natural cultivation was used initially due to its low capital cost, artificial cultivation is more viable for fuel production on industrial scale. Environmental conditions are controlled using closed loop systems and key consumables, notably , water, and nutrients, are dispersed throughout the system as required. The system itself can take the form of either 'raceways' or tubes; however, both fundamentally do the same thing—circulate algae from storage into a light-rich environment so that photosynthesis occurs, then back into storage. Photosynthesis allows the algae to 'capture' the carbon from the bubbled into the system, or from the open air, while simultaneously releasing the oxygen attached to the carbon (Adeniyi et al., 2018).

(Lumen Learning, n.d.)

As the algae grows and reproduces, carbon will accumulate in the system in the form of glucose, and within the oils that algae produce to store energy long term. The oils produced by certain species of algae contain high content of lipids; a portion of which are fatty acids. Fatty acids are long hydrocarbon chains with a carboxyl group at one end.
Harvested biomass is processed, and oils are extracted. The dried biomass then undergoes pyrolysis, which converts any remaining compounds into bio-oil, and similar by-products to crude oil (U.S. Department of Agriculture, n.d.).

Processing/Synthesis of fuel

Processing of algal/bio-oils is less efficient than crude oils. Since the main source of hydrocarbon chains is fatty acids, the carboxyl group adds a significant amount of oxygen to the reaction mixture. While pyrolysis of crude oil is often aided by a catalyst, effective pyrolysis of bio oils requires one.

Wang et al. (2014) demonstrated the poor cracking performance, and investigated the effect of temperature, pressure, additives, and presence of a catalyst on the yield of high-grade hydrocarbon fuels. It was found that the addition of ethanol to the cracking mixture improved yields significantly. Ethanol improves the (Hydrogen to carbon effective ratio) of reactants, which was previously found to improve cracking performance. Furthermore, the oxygen present in the hydroxyl group () is likely to join with excess carbon to form compounds and , as opposed to forming (acetic acid) or other by-products/coking agents.

Ethanol

At , and of the product was hydrocarbons and aromatic hydrocarbons by weight respectively. While coking did occur, use of the catalyst HSZM-5 improved yields, and was stable enough for coke removal to be achieved through combustion, allowing for reuse of catalyst. The high hydrocarbon content of the final product is commendable; however, this does not equate to a high yield. While the overall selectivity, or ratio of oil weight to final usable product weight, was , this is lower than crude oil's when it is cracked to form components of similar high-quality fuel at lab scale (Akah et al., 2025).

Overall, while bio-oil derived from algal sources has a lower energy content, due to high oxygen presence in fatty acids, cracking performance is shown to be excellent at lab scale, and strongly resembles current crude oil cracking operations at large scale. While yield by weight is lower, it is still competitive considering the technology discussed is still in its infancy, and has potential for development and industrialisation.

Performance

criteria

Exhaust gas temperature and power

When complete combustion occurs, all hydrocarbon bonds are broken, and reformed into and . This results in the maximum amount of energy being released. The conversion of liquid fuels into gasses, and the rapid release of energy as heat result in increased cylinder pressure, and therefore more 'power' being generated by the engine.

While the output of an engine can be measured using a dynamo, this gives in incomplete picture of how much combustion is actually occurring. Therefore exhaust gas temperature (EGT) is also measured. A higher exhaust gas temperature generally means that a larger portion of combustion is occurring with optimal stoichiometric ratios. When fuels have similar energy content, exhaust gas temperature can be directly compared to determine which fuel has more desirable combustion characteristics.
(Ge et al., 2022)

Metrics

Ge et al. (2022) compared the performance of a cooking oil derived bio gasoline created using similar cracking techniques. Studies on the combustion characteristics on algal derived fuels are sparse, but the bio oil the fuels are derived from both contain similar fatty acids, and once pyrolysed, their products are nearly identical in terms of hydrocarbon make up.

(Ge et al., 2022)

It was found that as biogasoline proportion of the fuel increased, both power, and EGT increased in a loosely quadratic manner. At lower concentrations, such as , biogasoline exceeds the performance of regular gasoline alone, and demonstrates higher power, and EGT. This indicates that this blend combusts more completely, and offers superior performance to gasoline alone.
However once the biogasoline concentration was increased to , and beyond, decreases in power and EGT are apparent. The difference between the power generated by the best, and worst performing blends was at most , which was roughly of the engines total rated capacity.

(Ge et al., 2022)

It is hypothesised that the biogasoline raised the octane of the fuel, and therefore made less susceptible to premature ignition. This is based on the significantly higher flash point of the fuel. It was also found that the biogasoline had a higher viscosity than regular gasoline. It is thought that the higher viscosity could have lead to insufficient vaporisation, and therefore incomplete or inefficient combustion.

The caloric value of biogasoline was found to be only of unleaded gasoline, which somewhat accounts for the lower performance, however this is clearly not the only factor at play; As mentioned before, the blend performed better than gasoline alone.

Burning Emissions

A closely related topic is the fuel's burning emissions. As mentioned previously, combustion characteristics differ between fuels. The amount of fuel being burnt daily is tremendous; Transitioning to a fuel with higher emissions will multiply even the smallest difference many times. Further considering the lower energy content of biogasoline, more fuel will be required to release the same amount of energy, therefore higher greenhouse gas (GHG) or nitric oxide () emissions per gram will further contribute to the issue.

It should be mentioned that while the carbon released from combustion of biogasoline is derived from the atmosphere and therefore "net zero". Tailpipe emissions of aren't necessarily a concern, however, and emissions require investigation, as both have much higher potential to harm people. emissions in particular are exceedingly concerning, as they can form nitric acid rain, and are not reabsorbed during algae production.

(Ge et al., 2022)

(Aakko-Saksa et al., 2011)

Considering the previously cited study by Ge et al. (2022), and Aakko-Saksa et al. (2011), a clear trend can be observed.
When percentage of biogasoline , emissions are reduced. As biogasoline fraction increases so that biogasoline content , emissions increase to match, or exceed under high load as shown in figure X, the emissions of gasoline.

Limitations

• Lab Scale
  

Conclusion

May not be a drop in replacement, as it does not work in cold climates